A stone of 1 kg is thrown with a velocity of 20 ms-1 across the frozen surface of a lake and comes to rest after travelling a distance of 50 m. What is the force of friction between the stone and the ice?

Given, mass of the stone (m) = 1 kg

Initial velocity (u) = 20 m/s

Terminal velocity (v) = 0 m/s
{as stone reaches a position of rest}

Distance travelled by the stone (s) = 50 m

We know that, \( v^2 - u^2 = 2 a s \)
\(\Rightarrow \) acceleration of stone \( = \frac{0 - 400}{100} = - 4 m/s^2 \)

Now, F = ma
\(\Rightarrow \) force acting om stone = 1 × (-4) = -4N